You need a good barrel wrench- bushamaster and dpms sell some good ones. Don't get the cheapest kind, get a big steel wrench.
Next, you need a good bench, and a clever way to solidly attach your upper to the bench. Lots of soft pine 2x4s and lag bolts works for me. Crude, but effective.
Otherwise, a big vise and fixture to hold the upper. $. Lag bolts and 2x4s looks pretty good.
Maybe Kroil or other penetrating oil. How old is your upper, in rounds?
Well, soak threads in kroil, in case you feel unlucky.
Lefty loosy, righty tighty.
You do not need a torque wrench for anything!
Let the flame wars begin
Pete

Thanks guys! The upper is a 98 vintage BM Vmatch, with 24" bbl and round BM aluminum ff fore-end. Probably close to 300 rounds.
I guess I have to remove the gas tube first....which means I have to remove the the front sight post (which is flat, not a sight) by removing the two lower pins right?
Will the gas tube then just slip out?
Will I have to remove the barrel? The Badger unit looks like a two part, and the instructions make me believe that the bbl needs to come off first??
Sorry for the dumb questions guys; I just don't want to mess anything up. :)

You will have to remove your barrel, no question about it. This is an easy job if you have a barrel wrench and a well anchored vise.
The gas tube just slips out after you remove the pin off the front sight post. Just pull it out of the post and into the receiver until it clears the post, then yank it out of the receiver. You might have to use a pair of plyers to coax and twist it out. After the tube is out, set the barrel on the vise and tighten really good (wrap the barrel in a sheat of leather to avoid scratches). Use the wrench to loosen the nut inside the delta ring; after removing the nut, the barrel will slide out.
The hard job will be to remove the front sight post. You need to put the post on a vise, upside down and with the barrel in a horizontal position. You'll need a correctly sized punch and a hammer to drive the pins out, which is no easy task. Most pins are tapered and only come out from one side, so make sure you push the smaller end. Some pins are straight, so it doesn't matter. After the pins are out, oil up the base at the barrel and carefully twist it out, trying to to scratch the finish too bad.
Of course, the delta ring assembly and barrel nut need to be removed also. They will just slide out after the front sight is removed.
To reassemble, reinstall the barrel on the receiver, slide in the nut of the floating handguard and tighten onto the receiver, making sure the holes align with the hole on the receiver. Now screw in the handguard. At this time install the gas tube on to the sight post. Slide the post back into the barrel, which is a tricky operation as the gas tube needs to line up perfectly with the hole in the handguard nut. Different people use different techniques to make the alignment easy, like sticking a shishkaboob stick into the receiver end of the tube, etc. After everything is is place, drive the pins back into the sight post holes.
Good luck!

Okay, got the gas block off. Got the gas tube out.
Looks like the BM free float tube is a one-piece unit. Also looks like there was some kind of white grease/lock-tite stuff where the fore-end connects to the receiver. I soaked the area in Kroil. I even used heat to the area. The handguard will not budge!!!!
I actually broke two strap wrenches in the process. :(
You sure it's lefty loosy/righty tighty?
Did I miss a step somewhere?
And no, the barrel nut wrench will not fit in the holes from behind the handguard while attached to the receiver.
SOS!

agony,
The handguard has to be two piece, otherwise there would be no way to tighten it onto the receiver with the barrel wrench. To unscrew, you should turn it counterclockwise as you look into the muzzle. How are you holding down the receiver while you try to unscrew the guard?
If the threads are seized, you might have no choice but to get a receiver clamp, stick it in a vise, and put the monkey wrench to the guards. But since it is not my rifle, I can only recommend that you go see your nearest gunsmith.

Thanks MADM16A1....
Actually, after solving the white grease mystery via an email from Bushmaster (very helpful and quick response, btw)--they use Tetra grease between the receiver and the fore-end, I got it off!!!! WOOOOOO HOOOOOO!!!!
It is a one piece tube. I had to wrap the guard in tape, and take the monkey wrench to it. The receiver was in a vice, in an armorers block. It took a whollop of a twist to get it off. I did put a couple gouges into the tube, but no biggie.
The Badger unit is a two piece and went on without a hitch. Shot the rifle yesterday and found it a much better platform when shooting from a Sinclair benchrest.
moral of the story:
One piece tubes SUCK. You don't need the barrel wrench for a one piece.
moral#2:
I need to sacrifice a goat to the person who invented the plumber's wrench....the greatest non-battle implement ever devised.
moral#3:
You guys are great...thanks for the help!
:)